Corrosion inhibitor

ABSTRACT

AQUEOUS ACID SOLUTIONS ARE INHIBITED AGAINST CORROSION OF METALS, ESPECIALLY FERROUS METALS, BY INCORPORATION OF A CORROSION-INHIBITING SYSTEM COMPOSED OF A COMBINATION OF AN ACETYLENIC CARBINOL AND A SATURATED HETEROCYCLIC NITROGEN COMPOUND MIXTURE DERIVED FROM GILSONITE.

United States Patent 3,591,512 CORROSION INHIBITOR Morton W. Leeds,Murray Hill, N.J., assignor to Air Reduction Company, Incorporated, NewYork, NY. No Drawing. Filed Dec. 31, 1968, Ser. No. 788,997

Int. Cl. C23g 1/06 U.S. Cl. 252-148 3 Claims ABSTRACT OF THE DISCLOSUREAqueous acid solutions are inhibited against corrosion of metals,especially ferrous metals, by incorporation of a corrosion-inhibitingsystem composed of a combination of an acetylenic carbinol and asaturated heterocyclic nitrogen compound mixture derived from gilsonite.

This invention relates to the inhibition of metal corrosion in acidicsolutions and is more particularly concerned with inhibited aqueous acidsolutions suitable for the treatment of metals.

Metal cleaning baths and pickling baths generally comprise aqueoussolutions of inorganic acids such as sulfuric acid, hydrochloric acid,and phosphoric acid, and are useful in the cleaning and treatment ofiron, zinc, ferrous a1- loys, and the like.

In the use of aqueous acidic baths to treat metals, additives orinhibitors in the baths are desirable to prevent or inhibit corrosion orerosion of the metal surfaces. Similarly, in the field of oil-wellacidizing, it is necessary to use inhibitors in order to preventcorrosion of the oil-well equipment by the aqueous acid solutionsemployed. Various other industrial operations also involve contactbetween an aqueous acidic solution and a metal, and an inhibitor must beused in order to minimize corrosion and/or consumption of the metal bysuch contact.

If no corrosion inhibitor is present when the aqueous acidic solutioncomes into contact with the metal, exessive metal loss, production ofundesirable metal surface properties, excessive consumption or loss ofacid, and,like adverse results will be experienced. Many different typesof inhibitors have been proposed, but there has been a continuing searchfor corrosion inhibitors which can be used effectively in smallconcentrations, and which are economical to produce, since the use ofinhibitors is a necessary expense and it is economically prudent to keepthis expense at a minimum while, at the same time, realizing the desiredinhibition of metallic corrosion or consumption. The need is also forcorrosion inhibitors which are effective at high temperatures, eg 200 F.and above, such as are encountered in various operations involvingacidic solutions, particularly oil-well acidizing where higher andhigher temperatures are encountered as the well extends further into theearth.

While various corrosion-inhibiting agents have been proposed, all ofsuch agents are not of equal effectiveness and of the many hundreds ofagents which have been contemplated, only a few are sufficiently activeto be commercially attractive. This is particularly true in the case ofhigh-temperature operations. Some inhibitors which have been proposedare reasonably effective at low and moderate temperatures, but failcompletely when high temperatures are encountered.

There has, therefore, been a continuing search for more effectiveinhibitors, or for ways of making a given inhibitor more effective. Thissearch has involved the discovery of combinations of inlubitors whichact together to provide an inhibitor system. However, many of thesesystems involve relatively expensive components so that, While they maybe relatively effective in their corrosioninhibiting activity, there aredisadvantages from an eco- 3,591,512 Patented July 6, 1971 nomicstandpoint, particularly if they have to be used in substantialquantities in order to bring about the desired corrosion-inhibitingactivity. Similarly, many of these systems are ineffective at elevatedtemperatures. In particular, there is a need for a corrosion-inhibitingsystem comprising a plurality of components wherein relativelyinexpensive compounds of poor corrosion-inhibiting action can becatalyzed or potentiated by the other component or components of thesystem so that the combination has a high corrosion-inhibiting activityeven at elevated temperatures.

It is accordingly an object of this invention to provide a novelcorrosion-inhibiting system involving a combination of agents which ishighly effective from the standpoint of corrosion-inhibiting activityand which is, at the same time, commercially attractive.

It is a further object of this invention to provide a novelcorrosion-inhibiting system comprising a combination of agents whereinone agent has a strong potentiating or cata lyzing action upon the otheragent so that the corrosioninhibiting effectiveness of the combinationis greater than the additive action of the components of thecombination.

It is another object of the invention to provide a corrosion-inhibitingsystem of the character indicated which is effective at hightemperatures.

In accordance with this invention, it has been discovered that the aboveand other objects can be achieved by the provision of acorrosion-inhibiting system comprising a combination of an acetyleniccarbinol of the formula RCHOHCECH, wherein R is a lower alkyl radical,i.e. containing up to 7 carbon atoms, which may form a straight chain ora branched chain, and a saturated heterocyclic nitrogen compound mixturederived from gilsonite. While any of the acetylenic carbinols fallingwithin the above formula are suitable, l-hexyn-S-ol, wherein R=3, and4-ethyl-l-octyn-3-ol, wherein R=7, have been found to be particularlysuitable. The saturated nitrogen compound mixture is obtained by thehydrogenation of the unsaturated heterocyclic nitrogen compound mixturedirectly derived from gilsonite which generally can have a distillationrange of about 350 F. to about 700 F., but most suitably there areemployed fractions cut from this overall range by fractionaldistillation and hydrogenated, as will be described below. Hydrogenationdoes not appreciably change the distillation range of the mixtures. Ahydrogenated mixture or fraction of gilsonitederived heterocyclicnitrogen compounds having a distillation range generally lying betweenabout 350 F. and 600 F. is preferably used. All temperatures are at 760mm. While the mixture is referred to as being composed of saturatedheterocyclic nitrogen compounds, it will be understood that minoramounts of the corresponding unsaturated compounds may be present as aresult of incomplete hydrogenation. The ratio between the acetylenicalcohol component and the saturated heterocyclic nitrogen compoundmixture component of the corrosion-inhibiting system may vary, but thebest results are obtained with weight rations ranging between 1:10 and10: 1, preferably 1:5 and 5:1, and most suitably between 1:2 and 2:1.

The acetylenic alcohol-heterocyclic nitrogen compound mixture inhibtionsystem of this invention is useful, in general, in the inhibition ofcorrosion of metal surfaces in contact with aqueous mineral acidsolution, such as hydrochloric acid, sulfuric acid, and phosphoric acid,for example in the acidizing of oil wells, in electrolytic cleaningbaths, and electrolytic refining of metals, as well as in metal cleaningand pickling baths. The use of the acetylenic alcohol-nitrogen compoundmixture inhibitor system of this invention for corrosion inhibition ofmetals in aqueous mineral acid solutions is advantageous in that theacetylenic alcohol-nitrogen compound mixture system can be employed as acorrosion inhibitor over a wide and useful concentration range. Afurther advantage of this inhibitor system is that it may be used atelevated temperatures to provide good corrosion inhibition, even when inrelatively low concentration.

The most effective amount of the corrosion-inhibiting system to be usedin accordance with this invention can vary, depending upon localOperatiOn conditions. Thus, the temperature and other characteristics ofthe acid corrosive system may have a bearing upon the amount ofinhibitor to be used. The higher the temperature and/or the higher theacid concentration, the greater is the amount of corrosion inhibitorrequired to give optimum results. In general, however, it has been foundthat a concentration of the corrosion-inhibiting system of the inventionbetween 0.01 and 2%, preferably between 0.01% and 1.2%, by weight of theaqueous acidic solution is an effective corrosion-inhibitingconcentration, although higher concentrations can be used whenconditions make them desirable, with a concentration between 0.05% to0.75% by However, it is not intended to limit the invention to anyspecific use of acidic solutions or with respect to any specific metalor acid.

Gilsonite is a natural asphalt-like substance found in the Uinta Basinin Utah and, when coked by application of heat, which results in thedistillation of volatile materials, produces an oily distillate as thetemperature is increased. This distillate has an overall boiling rangeof about 350 up to about 900, although most of it boils below 700, andwhen it is refined by treatment with sulfuric acid, produces mixtures ofheterocyclic nitrogen compounds. These mixtures are generallyfractionally distilled to provide a series of fractions. Such fractionsderived from the Gilsonite distillate are sold by the American GilsoniteCompany of Salt Lake City, Utah. One of these fractions, soldcommercially under the trade designation GN-ZOO is catalyticallyhydrogenated, and this hydrogenated fraction, which is sold under thetrade designation GN-300, is suitably employed as one of the componentsof the system of this invention to provide the hydrogenated heterocyclicnitrogen compound content. The following are typical distillation rangesin F. (ASTM D-l58):

GN-ZOO Vol. percent: F. Start 361 448 492 514 532 550 End 579 GN-300Vol. percent: F. Start 351 10 444 30 479 50 503 70 526 90 552 End 592The exact composition of these fractions is not fully known, but it isbelieved that the principal components are as follows: GN-ZOO: alkylatedpyrroles, indoles, pyridines, and quinolines; GN300: primarilyring-saturated secondary amines, e.g. alkylated piperidines,quinolitlines,

4 pyrrolidines and indolines, the balance of the mixture being made upof unsaturated heterocyclic, alkylated, tertiary amines such asmethyl-substituted pyrrole, indole, pyridine, and quinoline.

The method used to determine the inhibiting properties of the system ofthe invention employs test specimens or coupons. To prepare the coupons,they are wiped with acetone to remove any residual oils or grease, andpickled for one minute in 10% hydrochloric acid to eliminate any scaleand surface film. After pickling, the coupons are dipped in sodiumbicarbonate solution, rinsed well in tap water, rinsed in distilledwater, and finally dried with acetone. The clean and dry specimens arethen Weighed to the nearest 0.1 mg. In carrying out the evaluation,hydrochloric acid of 15% by weight concentration is used in order toduplicate oil-well acidizing conditions. The inhibitor system is addedto 4 02. test bottles, ml. of the acid then added to each bottle; andthe mixture shaken vigorously. The bottles are suspended in aconstant-temperature bath consisting of a bell jar filled with ethyleneglycol and equipped with a stirrer. The temperature is regulated tomaintain the samples at 200i2 F. The bottles are placed in the bath /2hour before the test coupons are added to insure temperatureequilibrium. The weighed coupons, in duplicate, are then supported onglass hooks in the test bottles and the bottles are covered with watchglasses during the testing period of 16 hours. At the end of the testingperiod, the bottles are removed from the bath, the coupons withdrawn,rinsed with Water, sodium bicarbonate solution, distilled water, anddried in acetone, then weighed to measure weight loss.Corrosion-inhibiting properties are conveniently expressed as percentinhibition, using the following formula:

Percent, inhibition Percent inhibition Original wt. test coupon wt. lossof test coupon X100 original wt. test coupon The following experimentswill serve to illustrate the effectiveness of the corrosion-inhibitingsystem of this invention under severe corrosion conditions encounteredin practical application:

EXAMPLE Using the testing procedure described above, and employing testcoupons of mild steel 1 in. x 2 in. x in. in size, samples comprisingl-hexyn-3-ol or 4-ethyl-1-octyn- 3-01 in combination with a mixture ofsaturated heterocyclic nitrogen compounds as represented by a commercialfraction of the character described above, in 1:1 weight ratio, wereadded to 15% hydrochloric acid, each component of the combination beingadded in the amount of 0.12% by weight of the acid, and the combinationevaluated for corrosion-inhibiting activity. At the same time a blanktest, using the same acid but without any inhibitor, was made. Thefollowing results were obtained:

Percent inhibi- Inhibitor: tion, 16 hrs. l-hexyn-3-ol-l-GN-300 (0.24%)99+ 4-ethyl-l-octyn-3-ol-l-GN-3OO (0.24%) 99+ None These tests show thepositive action of the combination of an acetylenic carbinol and amixture of saturated heterocyclic nitrogen compounds in accordance withthis invention in inhibiting metal corrosion in an acid solution of highconcentration at an elevated temperature only Slightly below the boilingpoint of water, over a prolonged period of time, the components of thesystem being relatively inexpensive chemicals in thecorrosion-inhibiting field. Corresponding results are obtained whenother acetylenic carbinols and other saturated nitrogen compoundmixtures within the definitions set forth above are employed in formingthe inhibiting system of this invention.

The coupons used in the foregoing experiments were cut from a ,4 in.sheet of a mild steel having the follow ing typical analysis: 0.15% max.carbon, 0.30-0.60% manganese, 0.04% phosphorus, 0.05% sulfur, thebalance 1ron.

It will be understood that various changes and modifications may be madein the operations described in the foregoing without departing from thescope of the invention as defined in the appended claims. It isintended, therefore, that all matter contained in the above descriptionof the invention shall be interpreted as illustrative only and not aslimitative.

I claim:

1. A metal corrosion-inhibitor system for use with aqueous mineral acidswhich consists essentially of an acetylenic carbinol of the formulaRCHOHCECH, wherein R is a lower alkyl group, and a saturatedheterocyclic nitrogen compound mixture derived from gilsonite anddistilling within the range of about 350 F. and about 700 F. at 760 mm.Hg, said acetylenic carbinol and said mixture being in the relativeweight ratios of 1:10 and 2. A corrosion-inhibited mineral acidconsisting essentially of an aqueous solution of the mineral acid and asmall but eifective amount of a corrosion-inhibiting system consistingessentially of an acetylenic carbinol of the formula R-CHOHC CH, whereinR is a lower alkyl group, and a saturated heterocyclic nitrogen compoundmixture derived from gilsonite and distilling within the range of about350 F. and about 700 F. at 760 mm. Hg, said acetylenic carbinol and saidmixture being in the relative weight ratios of 1:10 and 10: 1.

3. A corrosion-inhibited acid as defined in claim 2, wherein saidcorrosion-inhibiting system is present in the amount of 0.01% to 2% byweight.

References Cited UNITED STATES PATENTS 3,107,221 10/1963 Harrison et al252-148 3,249,548 5/1966 Herman et a1 252148X 3,404,094 10/ 1968 Keeney252148 3,432,527 3/1969 Malec et a1 252392 MAYER WEINBLA'IT, PrimaryExaminer U.S. Cl. X.R.

